1. Field of the Invention
The present invention relates to a fixation device, a fixation method, an image forming apparatus, an image forming method and a fixation fluid.
2. Description of the Related Art
An image forming apparatus such as a printer, a facsimile machine and a copying machine is an apparatus for forming an image containing a character or a symbol on a recording medium such as paper, cloth and OHP sheets, based on image information. Particularly, an electrophotographic image forming apparatus has widely been used in offices since a highly fine image may be formed on a normal paper sheet at a high speed. In such an electrophotograhpic image forming apparatus, a thermal fixation process has widely been used in which toner is fixed on a recording medium by heating and fusing the toner on the recording medium and applying a pressure on the fused toner. The thermal fixation process has preferably been used since a high fixation speed and a high fixed-image quality may be provided.
However, a half or more of electric power consumed in such an electrophotographic image forming apparatus is used for heating toner in the thermal fixation process. On the other hand, a fixation device with low electric power consumption (energy saving) is desired from the viewpoint of dealing with environmental problems in recent years. That is, it is desired to extremely lower the temperature of heating of toner to fix the toner more than ever before, or to provide a fixation method which does not require toner heating. Particularly, a non-heating fixation method for fixing toner on a recording medium while no toner is heated at all is ideal in view of the low electric power consumption.
For such a non-heating fixation method, for example, Japanese Patent No. 3,290,513 suggests a wet-type toner fixation method which includes spraying or dropping an oil-in-water-type fixing agent in which an organic compound being capable of dissolving or swelling toner and insoluble or difficult to dissolve in water is dispersed and mixed in water, onto unfixed toner provided at a predetermined position on a surface of a substrate so as to dissolve or swell the toner, and subsequently drying the substrate.
However, since the oil-in-water-type fixing agent in which an organic compound being insoluble or difficult to dissolve in water is dispersed and mixed in water is used in the wet-type fixation method disclosed in Japanese Patent No. 3,290,513, a recording medium (substrate) such as a transcription paper sheet may absorb the water and thereby cockling or curling may occur on the recording medium when a large amount of the fixing agent is provided to unfixed toner. Accordingly, stable and high speed conveyance of a recording medium which is required for an image forming apparatus may be significantly disturbed. Herein, if the water is removed from the fixing agent provided on the recording medium by evaporating a large amount of water contained in the fixing agent using a dryer, a electric power would be required which is comparable with the electric power consumption of an image forming apparatus using a thermal fixation process.
Furthermore, for a fixation liquid which does not repel water-repellent treated and unfixed toner, some oily fixation liquids have conventionally been suggested in which a material for dissolving or swelling toner is dissolved in an oily solvent. For one example of them, for example, Japanese Patent Application Publication No. 2004-109749 suggests a fixation liquid in which, for example, an aliphatic dibasic acid ester as a material component for dissolving or swelling a resin component constituting toner is diluted (dissolved) in non-volatile dimethylsilicone as a diluent (solvent). Also, Japanese Patent Application Publication No. 59-119364 suggests a solution for fixing an unfixed toner image which may be used for a fixation method capable of fixing an unfixed image formed by an electrostatic method on an image-receiving sheet sharply and easily without causing an image irregularity, wherein 100 parts by volume of a solvent dissolving toner and having a compatibility with a silicone oil is compatibly mixed with 8-120 parts by volume of a silicone oil. Such oily fixation liquids may dissolve or swell toner without repel water-repellent treated and unfixed toner and fix the toner on a recording medium since an oily solvent having high affinity with the water-repellent treated and unfixed toner is contained.
Each of Japanese Patent Application Publication Nos. 2004-109749 and 59-119364 discloses a configuration for providing a liquid onto unfixed toner. However, as shown in FIG. 17A, when the thickness of a fixation liquid layer 4 on an application roller 1 as a contact provision part is less than that of an unfixed toner layer 3 on a recording medium 2 in a configuration such that a fixation liquid is applied onto the unfixed toner layer 3 using the application roller 1, unfixed toner particles may be attracted by the surface tension of the fixation liquid layer on the surface of the application roller 1 at a position at which the application roller 1 moves away from the recording medium 2 and the toner particles may offset onto the application roller 1, whereby many irregularities may be caused on an image on the recording medium 2.
On the other hand, as shown in FIG. 17B, when the thickness of a fixation liquid layer 4 on an application roller 1 is sufficiently greater than that of an unfixed toner layer 3, the surface tension of the liquid layer on the surface of the application roller 1 may become not easy to act on toner particles directly and the toner may become not easy to offset onto the roller, at a position at which the application roller 1 moves away from a recording medium 2 because of a large amount of the liquid. However, since a large amount of the fixation liquid is applied on the paper surface, the toner particles may be carried away on the recording medium 2 due to an excess of the fixation liquid so as to cause degradation of image quality or a drying time period may become longer so as to cause a problem in the fixation responsibility. Also, significant residual liquid feeling (wet feeling obtained when a hand contacts a paper sheet) may be caused on the paper sheet. Furthermore, when the fixation liquid contains water and the amount of application onto a cellulose-containing medium such as a paper sheet is large, the recording medium such as a paper sheet may significant curl and jam of a paper sheet may occur at the time of conveyance of a recording medium such as a paper sheet in an apparatus such as an image forming apparatus. Thus, in the configuration of conducting roller application with such a fixation liquid, it may be very difficult to attain both application of a small amount of a fixation liquid onto a toner layer on a paper sheet for improvement of fixation responsibility, reduction of residual liquid feeling and prevention of curling, and prevention of toner offset onto a fixation roller. Also, when a die coat device, a blade application device, or a wire bar application device are used for a contact application part, toner may offset on the contact application part due to the surface tension of a fixation liquid in the case of a small amount thereof.
As described above, it may be very difficult to attain both application of a small amount of a fixation liquid onto a toner layer on a paper sheet for improving fixation responsibility and uniform application without causing an irregularity of a toner image, by the contact application part and the conventional formulation of a fixation liquid.